The ability of a person (most commonly a male) to enter a state of sexual arousal and/or sexual climax (i.e. ejaculation) simply by imagining a sexual situation that would normally induce said sexual reaction; when experienced during sleep, also referred to as a nocturnal emission or "wet dream".

WARNING: The typical high school male is prone to fits of psycholagny when within about 10-ft. range of anyone on whom they have a crush, including peers and/or teachers. You have been warned.